Over the last four years, Mexicans have learnt that waging a war against organised crime not only takes a toll on human life at home, but also impacts on the complex and sometimes ambivalent relationship with their northern neighbour.

There have been promises to work together against the drug traffickers, triggered by fears in Washington that the violence will spill over into United States (US) territory, and an acknowledgement by both countries that they share responsibility for the problem. The battle against the drug gangs in Mexico has come to dominate the bilateral relationship.

In December 2006, Mexican President Felipe Calderon, who had just been inaugurated after a tightly contested presidential election, launched a head-on crack down on the drug traffickers who use Mexico to get illegal narcotics into the US. More than four years on, nearly 35,000 people have been killed in drug related violence and an increasing number of Mexican states - many of them along the border with the US - have been engulfed in the conflict. Meanwhile, there is little evidence that the flow of drugs into America has slowed or that the cartels in Mexico are weakening. With 15,273 people killed in 2010 alone - the bloodiest year of the offensive - many sectors of Mexican society are calling for a change in the government's strategy.

Washington, however, has firmly supported Calderon's policies, celebrating successes like the capture or killing of several high profile drug barons, and providing close cooperation in the shape of financial aid, intelligence sharing and provision of surveillance equipment. US Secretary of State Hillary Clinton used a recent visit to Mexico - the third in two years- to provide yet another ringing endorsement. Describing herself as a "fan" of President Calderon, she said that there is "no alternative" to the military confrontation against the traffickers.

Turbulence

Washington may applaud the strategy, but there have been signs recently that the US is concerned at the lack of tangible results. Clinton herself, speaking at a think tank in Washington last September, said that drug cartels in Mexico are showing more and more signs of becoming "an insurgency" and that Mexico is increasingly looking like the drug-ravaged Colombia of the 1980s. The comparison irked the Mexican government, which categorically denied Clinton's statement, and President Barack Obama himself came out to play down the remarks made by his Secretary of State.

In February, the Under Secretary of the Army, Joseph Westphal, raised similar concerns during a session at the University of Utah. When asked about the areas of concern for US foreign policy, he referred to "a form of insurgency in Mexico with the drugs cartels that's right on our border," and added, "this is about, potentially, a takeover of government by individuals who are corrupt." Again the outrage from Mexican officials forced Westphal to issue a statement retracting what he called his "inaccurate" comments.

Probably the harshest words by US officials regarding the security situation in Mexico emerged in documents that were never meant to be read by the general public. The diplomatic cables from the US embassy in Mexico City, released by WikiLeaks, reflected increasing dismay among US officials over Mexico's lack of progress in its combat against drug trafficking organisations. Some of the wires harshly criticised specific parts of the effort. The Mexican army was described as "slow and risk averse", and cooperation between Mexico's security agencies was lambasted, with institutions like the Army, Navy and Federal Police, as one of the wires said, "often locked in a zero-sum competition in which one agency's success is viewed as another's failure, information is closely guarded and joint operations are all but unheard of."

The cables released, however, did include praise for Mexico's tough approach to the criminal groups, and they urged for further bilateral cooperation. Through the Merida Initiative, Mexico already has received millions of dollars from Washington in equipment, training, and joint work in special operations. Although the financial aid has not been delivered at the pace that many Mexicans hoped for when the initiative was first launched in 2007, US support is believed to have been crucial, for example, in captures of drug barons like Arturo Beltran Leyva in December 2009.

Few think this will change after, in mid-February of this year, two agents of the US Immigration and Customs Enforcement agency assigned in Mexico City were shot by unknown assailants as they were driving from the Mexican capital to the northern city of Monterrey. One of the agents, Jaime Zapata, was killed, and the other was injured. It may take some time to know whether that attack has any link with organised crime; both countries quickly promised to cooperate to bring the perpetrators to justice. This presented a stark difference from the 1985 killing on Mexican soil of Enrique Camarena, a US Drug Enforcement Agency (DEA) official, at the hands of drug cartel members. That murder and the investigations that followed - in which Mexican officials were accused by the US of protecting the killers - caused deep strains between both governments, bringing the bilateral relationship to a historic low.

Shared Problem, Shared Solution?

Under the Obama administration, Mexico has achieved an important discursive milestone: US officials now openly admit to a 'shared responsibility' relating to the drug traffickers. As the world's largest consumer of illegal narcotics, the US's seemingly insatiable demand is acknowledged as an important part of the problem.

There is also the issue of weapons. It is now widely accepted that the majority of the firearms used by the cartels are bought in the US. The criminals take advantage of the liberal gun ownership laws there and then smuggle their purchases back into Mexico. Since 2006, Mexico has confiscated almost 100,000 weapons from the cartels - and, according to a 2009 report by the US Government Accountability Office, more than ninety percent of firearms seized in Mexico between 2006 and 2009 came from the US. This is why President Calderon has pushed for tougher gun control laws in the US, such as reinstating the ban on assault weapons that expired in 2004 and was never renewed by American authorities.

With presidential elections due in both countries in 2012, and the gloomy forecasts of an increase in the violence, the Mexican drug traffickers are likely to be on both electoral agendas. Trying to ensure victory for his centre-right National Action Party, Calderon will most probably focus on the achievements of what is set to become the main legacy of his six year administration: 19 of 37 drug barons captured or killed so far; more than ten billion dollars worth of narcotics confiscated from the cartels; and some dents in the financial strength of the cartels, whose business amounts to an estimated forty billion dollars every year.

But even if both countries can point to some successes to offset the high death toll, the continuing violence, the inexhaustible demand and supply of drugs and the stream of replacement Mexican drug lords, the US and the region as a whole face a profound challenge. While the Andean nations continue to supply most of the narcotics and as the criminal groups feel the heat of the Mexican government's offensive, they simply move their operations elsewhere. While the Caribbean continues to battle similar problems, there are strong indications that the cartels are using several countries in Central America as a new base for their operations. Weaker states, laxer security enforcement and frail institutions in Guatemala, El Salvador and Honduras, combined with existing widespread corruption, provide the traffickers with the ideal setting for their illegal business. Washington is well aware and on his forthcoming visit to Latin America, President Obama will skip Mexico and head directly to Central America's smallest nation - El Salvador, a country already grappling with one of the highest homicide rates in the world. For many, this is yet another indication that the 'drugs war' being fought in Latin America is not going to be won anytime soon.

Julian Miglierini is BBC Correspondent for Mexico and Central America.